diff --git a/speed-transition.lua b/speed-transition.lua
index 6cc7340..d9d3605 100644
--- a/speed-transition.lua
+++ b/speed-transition.lua
@@ -19,7 +19,8 @@ function check_should_speedup()
    subdelay = mp.get_property_native("sub-delay")
    mp.command("no-osd set sub-visibility no")
    mp.command("no-osd sub-step 1")
-   nextsub = math.abs(mp.get_property_native("sub-delay"))-math.abs(subdelay)
+   nextsubdelay = mp.get_property_native("sub-delay")
+   nextsub = subdelay - nextsubdelay
    --print("nextsub in seconds "..nextsub)
    mp.set_property("sub-delay", subdelay)
    mp.command("no-osd set sub-visibility yes")